Just out of curiosity; I would like to see your own pages.
In other professions (web design, software development, etc) this is usually a sign of missing expertise. What kind of designer or programmer wouldn't proudly show his/her latest creations when asked to do so?
However, in this case there might be another reason. Maybe the customers don't want to be used as a reference? This leads to an interesting question:
Is it bad for business to publicly admit the use of SEO techniques?
You are right about publicly admitting to have used SEO. A lot of my clients have requested NDAs, but some haven't. Unfortunately for them, admitting to have used SEO in their minds devalues the company.